Growing numbers of perinatally HIV-infected (PHIV+) or HIV-exposed, but uninfected (PHIV-) youth are approaching young adulthood, an age increasingly recognized as one of the most challenging transition periods as youth begin to assume adult responsibilities and establish patterns of positive and risky health behaviors that carry through to later life. PHIV+ young adults are making critical choices about treatment, sex, relationships, and child-bearing having grown up with a chronic sexually transmittable virus. Yet, the literature is silent about strategies to improve behavioral health, including mental health, sexual and substance use risk behavior and adherence to antiretroviral treatment (ART), as well as reduce HIV transmission to others as this population transitions into young adulthood. This proposal is a competing continuation of Child and Adolescent Self-awareness and Health study (NIMHR01-MH6913, CASAH 1 and 2), in which we have prospectively followed PHIV+ and PHIV- youth across older childhood and adolescence, collecting data informed by our theoretical model, Social Action Theory (SAT) on individual, family, social, and contextual determinants of behavioral health. In the past 4.5 years, CASAH has resulted in 40 scientific presentations, 63 publications (36 manuscripts; 27 published abstracts), 4 manuscripts in submission, and data that supported 5 NIH-funded intervention studies. This competing continuation will extend this work to create the proposed, CASAH 3, resulting in a 12-year profile of the psychosocial determinants of behavioral health in PHIV+ and PHIV- youth. In CASAH 3, we will examine 1) the impact of HIV infection on behavioral health (mental health, sexual and substance use risk behavior) and transitions in young adulthood; 2) how critical risk and protective factors from earlier developmental stages, drawn from SAT, as well as a risk and resilience framework affect young adult behavioral health and transitions; 3) trajectories of behavioral health across adolescence and the influence of these trajectories on young adult transitions; and 4) (among PHIV+ youth) influences on adherence to ART and health care over time. Participants were originally recruited at ages 9-16 years from four medical centers in NYC. In CASAH 1, we collected data on youth and their caregivers at two time points, 18 months apart, and in CASAH 2, we followed the youth into older adolescence at three additional time points, one year apart. In CASAH 3, young adults, ages 18-26 years, will be re-recruited and interviewed at three annual visits. In addition, multiple indicators of adherence will be utilized, including monthly, unannounced phone-based pill counts, self-reports, and medical record data. CASAH is one of the few determinants studies that has directly informed mental-health and HIV-prevention interventions and service systems for PHIV+ adolescents in the US and global contexts. CASAH-3 offers a time-sensitive and unique opportunity to examine extended behavioral health trajectories from childhood to young adulthood, theoretically informed and modifiable predictors of these trajectories and young adult transitions, and the role of HIV, critical to much needed intervention development.